Xerographic safe-light



p 19, 1957 K. A. METCALFE ETAL 3,342,119

XEROGRAPHIC SAFE-LIGHT Fil ed Dec. 5. 1962 z zmc oxwe l% who . ANGSTEOM UNITS United States Patent 3,342,119 XEROGRAPHIC SAFE-LIGHT Kenneth A. Metcalfe, Fulham, South Australia, William H. Lowe, Beaumont, South Australia, and Alwin S. Clements, Largs Bay, South Australia, Australia, assiguors to The Commonwealth of Australia, the Secretary, Department of Supply, Melbourne, Victoria, Australia Filed Dec. 5, 1962, Scr. No. 242,556

Claims priority, application Australia, Dec. 8, 1961,

16 Claims. (Cl. 95-1) This invention relates to a xerographic safe-light.

In photography it is desirable to have a safe-light which will provide sufiicient illumination for ready manipulation of the photographic materials while in their sensitized form, yet will not destroy the image on the surface.

With silver halide it is found that safe-lights can be produced by selecting a band from the light spectrum to which the emulsion is insensitive, and if for instance certain silver halide coatings are handled under a red light, or a green light, no exposure of the coating will take place.

In xerography however, where a photoconductor medium is conditioned or acts to have the image produced on it by light, the same type of safe-light is not effective, and there has been a problem in arriving at a light which will give an illumination satisfactory for manipulation of the photoconductor coated medium yet will not bleed away the electrostatic image on the photoconductor medium.

' Wehave now found that a highly effective xerographic safe-light can be achieved by interposing between the light source and the photoconductor medium a translucent film of the photoconductor medium itself.

The film of photoconductor medium can be held in a resin or other base and can be coated on to the lamp itself which is to be used as the safe-light.

The principle of operation of our invention is that if a coating or film is interposed between a light source and the photoconductor medium, which is of the same nature as the photoconductor medium, the rays which would normally be absorbedby the photoconductor medium on which the image is being produced will similarly be absorbed by the film which as it is of the same material or nature as the photoconductor sheet will have the same absorption range.

In extensive tests which have been carried outwith safelights using the same medium for the filter element as is used on the sensitized sheet, it is found that a relatively strong visible light can be emitted without any danger of such light affecting the photoconductor medium, and therefore a highly effective safe-light is provided for xerographic purposes.

The thickness of the film used should be thin enough that the film is translucent, but thick enough that unfiltered light cannot penetrate directly between the particles of the photoconductor medium, and it has been found that for instances when using a photoconductor base or coating using say zinc oxide embedded in a resin of high electrical resistivity, the same medium is quite satisfactory as the coating for the safe-light, because the photoconductor has its absorption band in a specific re gion and that region is therefore the same for the safe-light film and for the photoconductor coating on which the image is being produced or developed.

In tests taken with a thin film of zinc oxide in a resin coating it was found that there is a strong absorption band in the region between 3600 and 3900 angstrom units, although it extends down less strongly to 3100 units, and again in the vicinity of 5100 angstrorn units, and therefore as the sensitivity to light modification of the photoconductor medium obviously lies Within the adsorption ranges mentioned, it follows that if the same photoconductor medium is used as a film for the safe-light, the safe-light will absorb rays in the same wavelength and these will therefore then not be available for modification of the image on the photoconductor medium itself, whereas light which is not readily absorbed by the photoconductor medium, in this case between about 400 angstrom units and 4900 angstrom units, has a relatively free passage through the photoconductor safe-light and forms a good illumination in the room. The fact that this wavelength is not absorbed by the zinc oxide in the safe-light, shows that it also is not absorbed by the zinc oxide in the film and merely passes through it without changing the electrostatic image.

The illustrations which accompany the specification show in FIG. 1 a schematic View one form of how the invention may be carried into effect; and in FIG. 2 a spectrum of zinc oxide absorption bands in angstrom units.

In FIG. 1 the glass wall or envelope 1 of the light source 2 surrounds the filament 3, the wall 1 having a coating SA on it of a photoconductor which is similar to the photoconductor coating 4 on the base 5 of the work piece. Filament 3 is a source of light of different wavelengths, many of which are visible and some of which are those to which coating 4 is sensitive.

In FIG. 2 the two absorption bands for a zinc oxide coating are designated 7.

It will of course be realized that the photoconductor coating can be applied to a transparent member interposed between the light source and the work piece which is being developed or otherwise handled, the actual shape or form of the safe-light shield being immaterial, the important feature being that the absorption bands of the photoconductor in the safe-light and the work piece are similar.

The amount of photoconductor in the coating, where the photoconductor is not of the continuous type (such as selenium) must be suchthat the unfiltered light does not pass between the photoconductor particles, and this can generally be achieved by having the photoconductor about four times the amount by volume in relation to the resin or other bonding medium.

Examples are given below of the composition and thickness of coatings on a safe-light:

Example 1 A paint is formulated as follows:

- Grams Alkyd resin Rhodene M8 50 Toluene Zinc oxide pigment (Durham microx) 200 Cobalt naphthenate 6% solution 0.5 Manganese naphthenate 6% solution 05 This liquid material is milled in a single roll mill for one hour and then applied to the surface of an incandescent lamp by dipping to form a film on the lamp. The of this film is 10 microns but 1 micron up to 100 microns may be used, 1 micron giving safety for 5 minutes and 100 microns giving safety for an indefinite period for zinc oxide electrophotographic paper.

Example 2 Substitute antimony trioxide for the zinc oxide in the formula of Example 1 where it is intended to use the safelight for antimony trioxide as a photoconductor in electrophotographic paper.

Example 3 Substitute cadmium sulphide for the Zinc oxide in the formula of Example 1 when it is intended to use the safelight for cadmium sulphide as an electrophotographic material.

Example 4 Substitute bismuth trioxide for the zinc oxide in the formula of Example 1 when it is intended to use the safelight for bismuth trioxide as an electrophotographic material.

Example 5 A lamp intended for use as a safe-light has a S-micron film of selenium vacuum evaporated on to its surface for use as a safe-light when selenium films or plates are used as the photoconductor.

What we claim is:

1. A xerographic safe-light comprising a translucent base and fixed thereon a photoconductor coating having its absorption bands coincident with the absorption bands of the photoconductor work piece being handled.

2. A xerographic safe-light according to claim 1 in which the photoconductor in the coating is the same as the photoconductor being handled.

3. A xerographic safe-light according to claim 1 wherein the photoconductor is a particulate material and is fixed to the said base by the photoconductor being dispersed in a film-forming bonding medium, the film-forming medium being less in volume than the particulate photoconductor.

4. A xerographic safe-light according to claim 1 in which the photoconductor is applied to the base as a continuous coating and has a thickness of about five microns.

5. A xerogr-aphic safe-light according to claim 1 wherein the photoconductor is a particulate material and is fixed to the said base by the photoconductor being dispersed in a film-forming bonding medium in the proportions by weight of about four parts of photoconductor to one part of bonding medium, and the film thickness is about ten microns.

6. A xerographic safe-light comprising a translucent base, a film-forming resin adhering to said base, and a photoconductor medium dispersed in said film-forming resin which includes the same absorption bands as the photoconductor medium being handled, the said photoconductor medium of the safe-light being in the proportion of about four parts by weight of photoconductor to one part by weight of resin and the thickness of the film being between one and one hundred microns.

7. A xerographic safe-light for use with zinc oxide photoconductor work pieces comprising a translucent base, a film-forming binder adhering to said base, and a zinc oxide photoconductor medium dispersed in said filmforming binder which has the same absorption bands as the photoconductor in the work piece, the said photoconductor medium of the safe-light being in the proportion of about four parts by weight of photoconductor to one part by weight of binder, and the thickness of the film being between one and one hundred microns.

8. A xerographic safe-light for use with zinc oxide photoconductor work pieces comprising a translucent base, a film-forming binder adhering to said base, and an antimony trioxide photoconductor medium dispersed in said film-forming binder which has the same absorption bands as the photoconductor in the work piece, the said photoconductor medium of the safe-light being in the proportion of about four parts by weight of photoconductor to one part by weight of binder, and the thickness of the film being between one and one hundred microns.

9. A xerographic safe-light for use with zinc oxide photoconductor work pieces comprising a translucent base, a film-forming binder adhering to said base, and a cadmium sulphide photoconductor medium dispersed in said film-forming binder which has the same absorption bands as the photoconductor in the work piece, the said photoconductor medium of the safe-light being in the proportion of about four parts by weight of photoconductor to one part by weight of binder, and the thickness of the film being between one and one hundred microns.

10. A xerographic safe-light for use with Zinc oxide photoconductor work pieces comprising a translucent base, a film-forming binder adhering to said base, and a bismuth trioxide photoconductor medium dispersed in said film-forming binder which has the same absorption bands as the photoconductor in the work piece, the said photoconductor medium of the safe-light being in the proportion of about four parts by weight of photoconductor to one part by weight of binder, and the thickness of the film being between one and one hundred microns.

11. In a xerographic process wherein a photoconductor material is to be charged and subsequently exposed to a light image to form thereon an electrostatic image, a method for providing a safe-light in which to handle said photoconductor material prior to the exposing of the same to said light image, said method comprising providing a source of light having visible light wavelengths in which said photoconductor material can be seen and thereby conveniently handled, and filtering out those of said wavelengths to which the photoconductor material is sensitive by interposing between the material and said source a filter made of said material, the wavelengths passing through said filter constituting said safe-light.

12. A method as claimed in claim 11 comprising forming said filter by dispersing said material in a bonding agent.

13. A method as claimed in claim 12 applying said material in said bonding agent to a light bulb constituting said source.

14. A method as claimed in claim 11 comprising forming an electrostatic charge on the first said material and processing the same in said safe-light.

15. A safe-light source for the convenient handling of a photoconductor material without influencing the electrostatic charges thereon comprising a light bulb including a source of various wavelengths of light at least some of which are visible and at least some of which are those to which the material is photoconductively sensitive, said bulb further including an envelope permeable to at least some of said wavelengths, and a filter of said photoconductor material operatively associated with said envelope to filter out those wavelengths to which the material is photoconductively sensitive.

16. A safe-light source as claimed in claim 15, wherein the filter constitutes a layer on said envelope.

References Cited UNITED STATES PATENTS 1,212,228 1/1917 John 240-20 2,962,374 11/1960 Dessauer 96-1 3,060,020 10/1962 Greig 96-1 FOREIGN PATENTS 589,325 12/1933 Germany.

JOHN M. HORAN, Primary Examiner, 

1. A XEROGRAPHIC SAFE-LIGHT COMPRISING A TRANSLUCENT BASE AND FIXED THEREON A PHOTOCONDUCTOR COATING HAVING ITS ABSORPTION BANDS COINCIDENT WITH THE ABSORPTION BANDS OF THE PHOTOCONDUCTOR WORK PIECE BEING HANDLED. 